A continuing purpose of this project is the study of Tyzzer's disease. The topics of present interest are: 1) characterization of the causative agent, Bacillus piliformis; 2) the serological response of the host to B. piliformis infection using the complement fixation test and fluorescent-antibody techniques; 3) the relationship of isolants from the rabbit and horse foal; 4) the pathogenesis of Tyzzer's disease in a variety of laboratory animals; 5) the stability of the spores of B. piliformis under a variety of conditions including temperature variation and contact with chemicals; and 6) the epidemiology of Tyzzer's disease with a view toward determining primary sources of infection in nature.